Exterior supported self-expanding stent-graft

ABSTRACT

This is a medical device and a method of using it. The device is a foldable stent-graft which may be percutaneously delivered with (or on) an endovascular catheter, via surgical techniques or using other suitable techniques and then expanded. The stent-graft uses a kink-resistant stent structure and an interior graft which is attached to the stent in such a way that the graft does not kink and yet the stent is able to conform to curves in the blood vessel lumen. The expandable stent structure preferably has a helically deployed torsional member with an undulating shape which is wound to form the generally cylindrical shape deployed as the stent. The helical winding desirably is aligned to allow undulations in adjacent turns of the helix to be in phase. The adjacent undulating shapes are held in that phased relationship using a flexible linkage, typically made of a polymeric material. The graft component cooperating with the stent is tubular and mounted on the interior of the stent. Although it may be made of any variety of materials, it preferably is an expanded polyfluorocarbon. The graft component may be bound to the flexible linkage which holds the stent windings in phase (or the stent structure itself) at a number of sliding attachment points.

This application is a continuation of 08/740,030 filed Oct. 23, 1996 nowabandoned which is a continuation of 08/299,190 filed Aug. 31, 1994 nowabandoned.

FIELD OF THE INVENTION

This invention is a medical device and a method of using it. The deviceis a foldable stent-graft which may be percutaneously delivered with (oron) an endovascular catheter or via surgical techniques or using othersuitable techniques and then expanded. The stent-graft uses akink-resistant stent structure and an interior graft which is attachedto the stent in such a way that the graft does not kink and yet thestent is able to conform to curves in the blood vessel lumen.

The expandable stent structure preferably has a helically deployedtorsional member with an undulating shape which is wound to form thegenerally cylindrical shape deployed as the stent. The helical windingdesirably is aligned to allow the undulations in adjacent turns of thehelix to be in phase. The adjacent undulating shapes may be held in thatphased relationship using a flexible linkage, typically made of apolymeric material. The stent may also be of a ring configuration. Thestent may be flared to promote smooth blood flow and to assure that thestent will remain in its chosen position.

The graft component cooperating with the stent is tubular and mounted onthe interior of the stent. Although it may be made of any of a varietyof materials, it preferably is an expanded polyfluorocarbon. The graftcomponent may be attached to the stent in a variety of ways butdesirably is bound to the flexible linkage which holds the stentwindings in phase (or to the stent structure itself) at a number ofsliding attachment points. This manner of attachment allows the stent toslide locally with respect to the graft structure or, in the case of thehelically wound stent structure, allows the adjacent undulating shapesin adjacent helical turns to slide longitudinally with respect to eachother as the stent is bent and still support the shape of the graft.

The stent-graft may be used to reinforce vascular irregularities, toprovide a smooth nonthrombogenic interior vascular surface for diseasedareas in blood vessels, or to increase blood flow past a diseased areaof a vessel by mechanically improving the interior surface of thevessel. The inventive stent-graft is especially suitable for use withinsmaller vessels between 2 mm and 6 mm in diameter but is equallysuitable for significantly larger vessels. The inventive stent-graft maybe self-expandable; it is kink-resistant, easily bent along itslongitudinal axis, and does not change its length during that expansion.

Included in the invention are methods for coupling the stent structureto the graft to optimize the flexibility and the kink resistance of theresulting stent-graft.

BACKGROUND OF THE INVENTION

Treatment or isolation of vascular aneurysms or of vessel walls whichhave been thinned or thickened by disease has traditionally been donevia surgical bypassing with vascular grafts. Shortcomings of thisprocedure include the morbidity and mortality associated with surgery,long recovery times after surgery, and the high incidence of repeatintervention needed due to limitations of the graft or of the procedure.Vessels thickened by disease are currently sometimes treated lessinvasively with intraluminal stents that mechanically hold these vesselsopen either subsequent to or as an adjunct to a balloon angioplastyprocedure. Shortcomings of current stents include the use of highlythrombogenic materials (stainless steels, tantalum, ELGILOY) which areexposed to blood, the general failure of these materials to attract andsupport functional endothelium, the irregular stent/vessel surface thatcauses unnatural blood flow patterns, and the mismatch of compliance andflexibility between the vessel and the stent.

Important to this invention is the use of less invasive intraluminaldelivery and, in a preferred aspect, placement of a nonthrombogenicblood-carrying conduit having a smooth inner lumen.

The most desired variations of this invention involve a stent-graftwhich is self-expanding, which does not shorten upon delivery, which hasexcellent longitudinal flexibility, which has high radial compliance tothe vessel lumen, and exposes the blood to a smooth, nonthrombogenicsurface capable of supporting endothelium growth.

The inventive device may be delivered in a reduced diameter and expandedto maintain the patency of any conduit or lumen in the body. An area inwhich the inventive stent-graft is particularly beneficial is in thescaffolding of atherosclerotic lesions in the cardiovascular system toestablish vessel patency, prevention of thrombosis, and the furtherprevention of restenosis after angioplasty. In contrast to many of thestents discussed below having metallic struts intruding into the bloodflow in the vessel lumen which generate turbulence and create bloodstasis points initiating thrombus formation, the smooth, continuoussurface provided by the preferred tubular inner conduit of our inventionprovides a hemodynamically superior surface for blood flow.

Mechanically, the linked helical stent structure used in the stent-graftprovides a good combination of radial strength and flexibility. Thestructure is also radially resilient. It can be completely crushed orflattened and yet spring open again once the obstructive loading isremoved. This ability is important for use in exposed portions of thebody around the peripheral vasculature or around joints. The stent-graftcan sustain a crushing traumatic blow or compression from the bending ofa joint and still return to the open configuration once the load isremoved.

With regard to delivery, the self-expansion mechanism eliminates theneed for a balloon catheter and the associated balloon rupture problemsoften associated with that delivery procedure. In addition, the absenceof the bulk of the balloon allows a smaller delivery profile to beachieved. Unlike some other self-expanding stent designs, thisstent-graft maintains a constant length throughout the expansionprocess. Thus, the stent-graft does not have some of the positioningproblems associated with other many self-expanding stents. In treatinglonger lesions, our self-expanding design eliminates the need forspecial long balloons or repositioning of the balloon between inflationsin order to expand the entire length of the stent.

The impermeability of the preferred stent-graft makes it suitable forshunting and thereby hydraulically isolating aneurysms. The expansileproperties derived from the stent structure provide a secure anchor tothe vessel wall.

Stents

The stents currently described in the open literature include a widevariety of different shapes.

Wallsten, U.S. Pat. No. 4,655,771, suggests a vascular prosthesis fortransluminal implantation which is made up of a flexible tubular bodyhaving a diameter that is varied by adjusting the axial separation ofthe two ends of the body relative to each other. In general, the bodyappears to be a woven device produced of various plastics or stainlesssteel.

U.S. Pat. No. 4,760,849, to Kroph, shows the use of a ladder-shaped coilspring which additionally may be used as a filter in certain situations.

Porter, U.S. Pat. No. 5,064,435, suggests a stent made up of two or moretubular stent segments which may be deployed together so to produce asingle axial length by a provision of overlapping areas. This concept isto permit the use of segments of known length, which, when deployed, maybe used together in overlapping fashion additively to provide a stent ofsignificant length.

Quan-Gett, U.S. Pat. No. 5,151,105, discloses an implantable,collapsible tubular sleeve apparently of an outer band and an innerspring used to maintain the sleeve in a deployed condition.

Wall, U.S. Pat. No. 5,192,307, suggests a stent having a number of holestherein and which is expandable using an angioplasty balloon so to allowratchet devices or ledges to hold the stent in an open position once itis deployed.

Perhaps of more relevance are the patents using wire as the stentmaterial.

Gianturco, in U.S. Pat. Nos. 4,580,568 and 5,035,706, describes stentsformed of stainless steel wire arranged in a closed zigzag pattern. Thestents are compressible to a reduced diameter for insertion into andremoval from a body passageway. The stents appear to be introduced intothe selected sites by discharge of the collapsed zigzag wireconfiguration from the tip of a catheter.

U.S. Pat. Nos. 4,830,003 and 5,104,404, to Wolff et al., shows a stentof a zigzag wire configuration very similar in overall impression to theGianturco device. However, the stent is said to be self-expanding andtherefore does not need the angioplasty balloon for its expansion.

Hillstead, U.S. Pat. 4,856,516, suggests a stent for reinforcing vesselwalls made from a single elongated wire. The stent produced iscylindrical and is made up of a series of rings which are, in turn,linked together by half-hitch junctions produced from the singleelongated wire.

Wiktor, U.S. Pat. Nos. 4,649,992, 4,886,062, 4,969,458, and 5,133,732,shows wire stent designs using variously a zigzag design or, in the caseof Wiktor '458, a helix which winds back upon itself. Wiktor '062suggests use of a wire component made of a low-memory metal such ascopper, titanium or gold. These stents are to be implanted using aballoon and expanded radially for plastic deformation of the metal.

Wiktor '458 is similarly made of low-memory alloy and is to beplastically deformed upon its expansion on an angioplasty balloon.

Wiktor '732 teaches the use of a longitudinal wire welded to each turnof the helically wound zig-zag wire which is said to prevent thelongitudinal expansion of the stent during deployment. A furthervariation of the described stent includes a hook in each turn of thehelix which loops over a turn in an adjacent turn.

WO93/13825, to Maeda et al, shows a self-expanding stent similar to theGianturco, Wolff, and Wiktor designs, formed of stainless steel wire,which is built into an elongated zig-zag pattern, and helically woundabout a central axis to form a tubular shape interconnected with afilament. The bends of the helix each have small loops or “eyes” attheir apexes which are interconnected with a filament. Because of theteaching to connect the eyes of the apexes, the stent appears to be adesign that axially expands during compression and may tear attachedgrafts because of the relative change in position of the arms of thezig-zag during compression of the stent.

MacGregor, U.S. Pat. No. 5,015,253, shows a tubular non-woven stent madeup of a pair of helical members which appear to be wound using opposite“handedness”. The stent helices desirably are joined or secured at thevarious points where they cross.

Pinchuk, in U.S. Pat. Nos. 5,019,090, 5,092,877, and 5,163,958, suggestsa spring stent which appears to circumferentially and helically windabout as it is finally deployed except, perhaps, at the very end link ofthe stent. The Pinchuk '958 patent further suggests the use of apyrolytic carbon layer on the surface of the stent to present a poroussurface of improved antithrombogenic properties.

U.S. Pat. No. 5,123,917, to Lee, suggests an expandable vascular grafthaving a flexible cylindrical inner tubing and a number of “scaffoldmembers” which are expandable, ring-like, and provide circumferentialrigidity to the graft. The scaffold members are deployed by deformingthem beyond their plastic limit using, e.g., an angioplasty balloon.

Tower, in U.S. Pat. Nos. 5,161,547 and 5,217,483, shows a stent formedfrom a zig-zag wire wound around a mandrel in a cylindrical fashion. Itis said to be made from “a soft platinum wire which has been fullyannealed to remove as much spring memory as possible.” A longitudinalwire is welded along the helically wound sections much in the same wayas was the device of Wiktor.

There are a variety of disclosures in which super-elastic alloys such asnitinol are used in stents. See, U.S. Pat. No. 4,503,569, to Dotter;U.S. Pat. No. 4,512,338, to Balko et al.; U.S. Pat. No. 4,990,155, toWilkoff; U.S. Pat. No. 5,037,427, Harada, et al.; U.S. Pat. No.5,147,370, to MacNamara et al.; U.S. Pat. No. 5,211,658, to Clouse; andU.S. Pat. No. 5,221,261, to Termin et al. None of these referencessuggest a device having discrete, individual, energy-storing torsionalmembers as are required by this invention.

Jervis, in U.S. Pat. Nos. 4,665,906 and 5,067,957, describes the use ofshape memory alloys having stress-induced martensite properties inmedical devices which are implantable or, at least, introduced into thehuman body.

Stent-Grafts

A variety of stent-graft designs are shown in the following literature.

Perhaps the most widely known such device is shown in Ersek, U.S. Pat.No. 3,657,744. Ersek shows a system for deploying expandable,plastically deformable stents of metal mesh having an attached graftthrough the use of an expansion tool.

Palmaz describes a variety of expandable intraluminal vascular grafts ina sequence of patents: U.S. Patent Nos. 4,733,665; 4,739,762; 4,776,337;and 5,102,417. The Palmaz '665 patent suggests grafts (which alsofunction as stents) that are expanded using angioplasty balloons. Thegrafts are variously a wire mesh tube or of a plurality of thin barsfixedly secured to each other. The devices are installed, e.g., using anangioplasty balloon and consequently are not seen to be self-expanding.

The Palmaz '762 and '337 patents appear to suggest the use ofthin-walled, biologically inert materials on the outer periphery of theearlier-described stents.

Finally, the Palmaz '417 patent describes the use of multiple stentsections each flexibly connected to its neighbor.

Rhodes, U.S. Pat. No. 5,122,154, shows an expandable stent-graft made tobe expanded using a balloon catheter. The stent is a sequence ofring-like members formed of links spaced apart along the graft. Thegraft is a sleeve of a material such as expanded a polyfluorocarbon,e.g., GORETEX or IMPRAGRAFT.

Schatz, U.S. Pat. No. 5,195,984, shows an expandable intraluminal stentand graft related in concept to the Palmaz patents discussed above.Schatz discusses, in addition, the use of flexibly-connecting vasculargrafts which contain several of the Palmaz stent rings to allowflexibility of the overall structure in following curving body lumen.

Cragg, “Percutaneous Femoropopliteal Graft Placement”, Radiology, vol.187, no. 3, pp. 643-648 (1993), shows a stent-graft of a self-expanding,nitinol, zig-zag, helically wound stent having a section ofpolytetrafluoroethylene tubing sewed to the interior of the stent.

Cragg (European Patent Application 0,556,850) discloses an intraluminalstent made up of a continuous helix of zig-zag wire and having loops ateach apex of the zig-zags. Those loops on the adjacent apexes areindividually tied together to form diamond-shaped openings among thewires. The stent may be made of a metal such as nitinol (col. 3, lines15-25 and col. 4, lines 42+) and may be associated with a“polytetrafluoroethylene (PTFE), dacron, or any other suitablebiocompatible material”. Those biocompatible materials may be inside thestent (col. 3, lines 52+) or outside the stent (col. 4, lines 6+). Thereis no suggestion that the zig-zag wire helix be re-aligned to be “inphase” rather than tied in an apex-to-apex alignment. The alignment ofthe wire and the way in which it is tied mandates that it expand inlength as it is expanded from its compressed form.

Grafts

As was noted above, the use of grafts in alleviating a variety ofvascular conditions is well known. Included in such known graftingdesigns and procedures are the following.

Medell, U.S. Pat. No. 3,479,670, discloses a tubular prothesis adaptedto be placed permanently in the human body. It is made of framework orsupport of a synthetic fiber such as DACRON or TEFLON. The tube is saidto be made more resistant to collapse by fusing a helix of apolypropylene monofilament to its exterior. The reinforced fabric tubeis then coated with a layer of collagen or gelatin to render the tubing(to be used as an esophageal graft) impermeable to bacteria or fluids.

Sparks, in U.S. Pat. Nos. 3,514,791, 3,625,198, 3,710,777, 3,866,247,and 3,866,609, teach procedures for the production of various graftstructures using dies of suitable shape and a cloth reinforcing materialwithin the die. The die and reinforcement are used to grow a graftstructure using a patient's own tissues. The die is implanted within thehuman body for a period of time to allow the graft to be produced. Thegraft is in harvested and implanted in another site in the patient'sbody by a second surgical procedure.

Braun, in U.S. Pat. No. 3,562,820, shows a biological prosthesismanufactured by applying onto a support of a biological tissue (such asserosa taken from cattle intestine) a collagen fiber paste. Theprocedure is repeated using multiple layers of biological tissue andcollagen fiber paste until a multi-layer structure of the desired wallthicknesses is produced. The prosthesis is then dried and removed priorto use.

Dardik et al, U.S. Pat. No. 3,974,526, shows a procedure for producingtubular prostheses for use in vascular reconstructive surgeries. Theprosthesis is made from the umbilical cord of a newly born infant. It iswashed with a solution of 1 percent hydrogen peroxide and rinsed withRinger's lactate solution. It is then immersed in a hyaluronidasesolution to dissolve the hyaluronic acid coating found in the umbilicalcord. The vessels are then separated from the cord and their naturalinterior valving removed by use of a tapered mandrel. The vessels arethen tanned with glutaraldehyde. A polyester mesh support is applied tothe graft for added support and strength.

Whalen, U.S. Pat. No. 4,130,904, shows a prosthetic blood conduit havingtwo concentrically associated tubes with a helical spring between them.Curved sections in the tube walls help prevent kinking of the tube.

Ketharanathan, U.S. Pat. No. 4,319,363, shows a procedure for producinga vascular prosthesis suitable for use as a surgical graft. Theprosthesis is produced by implanting a rod or tube in a living host andallowing collagenous tissue to grow on the rod or tube in the form ofcoherent tubular wall. The collagenous implant is removed from the rodor tube and tanned in glutaraldehyde. The prosthesis is then ready foruse.

Bell, U.S. Pat. No. 4,546,500, teaches a method for making a vesselprosthesis by incorporating a contractile agent such as smooth musclecells or platelets into a collagen lattice and contracting the latticearound a inner core. After the structure has set, additional layers areapplied in a similar fashion. A plastic mesh sleeve is desirablysandwiched between the layers or imbedded within the structure toprovide some measure of elasticity.

Hoffman Jr. et al, U.S. Pat. No. 4,842,575, shows a collagen impregnatedsynthetic vascular graft. It is made of a synthetic graft substrate anda cross-linked collagen fibril. It is formed by depositing a aqueousslurry of collagen fibrils into the lumen of the graft and massaging theslurry into the pore structure of the substrate to assure intimateadmixture in the interior. Repeated applications and massaging anddrying is said further to reduce the porosity of the graft.

Alonoso, U.S. Pat. No. 5,037,377, is similar in overall content to theHoffman Jr. et al patent discussed above except that, in addition tocollagen fibers, soluble collagen is introduced into the fabric. Asuitable cross-linking agent such as glutaraldehyde is used to bondadjacent collagen fibers to each other.

Slepian et al, U.S. Pat. No. 5,213,580, teaches a process described as“paving” or “stabilizing by sealing the interior surface of a bodyvessel or organ” by applying a biodegradable polymer such as apolycaprolactone. The polymer is made into a tubular substrate, placedin position, and patched into place.

Finally, there are known vascular grafts using collagenous tissue withreinforcing structure. For instance, Pinchuk, in U.S. Pat. Nos.4,629,458 and 4,798,606, suggests the use of collagen with some othertype of fibrous structure supporting the collagen as a biograft.Similarly, Sinofsky et al., U.S. Pat. No. 5,100,429, suggests apartially-cured, collagen-based material used to form a graft within ablood vessel.

Kreamer, U.S. Pat. No. 4,740,207, suggests a intraluminal graft made ofa semi-rigid resilient tube, open along a seam extending from one end tothe other, which is expanded within the vessel and which resultinglarger diameter is maintained by use of a ledge at the longitudinal seamfor catching the opposite side of the seam on the expanded graft.

The use of expanded polyfluorocarbons in vascular devices is shown inBritish patent Nos. 1,506,432, and 1,567,122, which patents show inparticular blood vessel linings of the material.

None of the cited references suggest a stent-graft similar to thatdescribed herein.

SUMMARY OF THE INVENTION

This invention is a foldable stent-graft which may be percutaneouslydelivered through or over a catheter, typically an endovascularcatheter, or using surgical techniques or other appropriatemethodologies.

The incorporated expandable stent structure utilizes torsional regionswhich allow it to be folded to a very small diameter prior todeployment. Preferably, the torsional members have an undulating shapewhich may be helically wound to form the stent's cylindrical shape. Theundulating shape may be aligned to allow the undulations in adjacentturns of the helix to be in phase. Adjacent undulating shapes may beheld in the phased relationship using a flexible linkage, often made ofa polymeric material. In the helically wound variation of the invention,the undulating torsional members do not have any means at (or near) theapex of the undulating shapes which would tend to constrict the movementof the flexible linkage during compression or bending of the stent. Thestent is preferably made of a highly flexible, superelastic alloy suchas nitinol, but may be of any suitable elastic material such as variousof the medically accepted stainless steels. The stent structure may alsobe of a series of rings incorporating the torsional members which ringsmay be axially linked.

The graft component used to complement the stent is typically tubular,placed within the stent, and may be made of a polymeric material whichmay be attached variously to the filament used to maintain the shape ofthe stent structure, when such filament is used, or to the stentstructure itself. Preferably, the graft component is a biocompatible,expanded polyfluoroethylene polymer. The attachment between the graftcomponent and the stent, e.g., by bonding the graft component to theflexible linkage or by using eyelets or other discrete or continuouslinking sites, is carefully crafted to allow the stent torsional membersto slide longitudinally with respect to each other and to the graftcomponent and so maintain the interior shape of graft. This is to saythat the graft component is supported at a variety of sites locatedalong its outer surface. Bending the stent-graft combination distributesthe flexing movement of the graft over a long region because of thedistributed support of the stent. The tendency of the graft component tokink in a single site is minimized and the resultant flexing is observedto take place in a collection of smaller non-kinking bends located amongthe tie points to the stent or the stent's filament.

The stent-graft may be used to reinforce vascular irregularities andprovide a smooth interior vascular surface, particularly within smallervessels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, 1C, 1D, and 1E are plan views of an unrolled stent formsuitable for use in the invention.

FIG. 2 is a side view of a stent suitable for use in this invention.

FIG. 3 is a close-up of a portion of the stent shown in FIG. 2.

FIGS. 4 and 5 show magnified portions of the inventive stent-graftdepicting methods of attaching the stent to the graft component.

FIG. 6 is a side view of the inventive stent-graft showing a variationhaving flared ends.

FIG. 7 shows a plan view of an unrolled stent produced from flat stock.

FIG. 8 shows a front quarter view of the rolled stent using the flatstock pattern shown in FIG. 7.

FIG. 9 shows a plan view of an unrolled stent produced from flat stockhaving a ringed structure.

FIG. 10 shows a front quarter view of the rolled ring structured stentusing the flat stock pattern shown in FIG. 9.

FIGS. 11, 12, and 13 show plan views of variations of unrolled stentsmade according to the invention.

FIGS. 14A-14C show a schematic procedure for deploying the inventivestent-grafts.

DESCRIPTION OF THE INVENTION

As was noted above, this invention is an expandable stent-graft and amethod of using it. The stent-graft is a combination of severalcomponents: first, a thin-walled tube forming the graft component whichgraft component is generally coaxial to and within the stent and,second, the expandable stent structure. The graft material mayoptionally contain a fibrous reinforcement material. The expandablestent structure is a cylindrical body produced either of a helicallyplaced (wound or otherwise preformed) torsion member having anundulating or serpentine shape or a series of axially situated ringscomprising those torsion members. When the undulating torsion member isformed into the cylinder, the undulations may be aligned so that theyare “in phase” with each other. The helically wound undulations aredesirably linked, typically with a flexible linkage of a suitablepolymeric or metallic material, to maintain the phased relationship ofthe undulations during compression and deployment and during bending ofthe stent. These stent configurations are exceptionally kink-resistantand flexible, particularly when flexed along the longitudinal axis ofthe stent.

Central to the invention is the distributed attachment of the stentcomponent to the graft component via, e.g., the bonding of the graft tothe filament which may used to maintain the stent in its tubular shapeor via bonding to other loops, eyelets, or fasteners associated with oradhering to the stent component.

The stent-graft may be delivered percutaneously, typically through thevasculature, after having been folded to a reduced diameter. Oncereaching the intended delivery site, it is expanded to form a lining onthe vessel wall.

Stent Component

Our stent is constructed of a reasonably high strength material, i.e.,one which is resistant to plastic deformation when stressed. Thestructure is typically from one of three sources:

1.) a wire form in which a wire is first formed into an undulating shapeand the resulting undulating shape is helically wound to form acylinder,

2.) an appropriate shape formed from a flat stock and wound into acylinder, and

3.) a length of tubing formed into an appropriate shape.

These stent structures are typically oriented coaxially with the tubulargraft component. The stent structures are, at least, placed on the outersurface of the graft although, in certain configurations, an additionalgraft structure may be placed on the outer surface of the stent. Whenthe outer graft structure is utilized, the stent structure should havethe strength and flexibility to tack the graft tubing firmly andconformally against the vessel wall. In order to minimize the wallthickness of the stent-graft, the stent material should have a highstrength-to-volume ratio. Use of designs as depicted herein providesstents which may be shorter in length than those often used in the priorart. Additionally, the designs do not suffer from a tendency to twist(or helically unwind) or to shorten as the stent-graft is deployed. Aswill be discussed below, materials suitable in these stents and meetingthese criteria include various metals and some polymers.

A percutaneously delivered stent-graft must expand from a reduceddiameter, necessary for delivery, to a larger deployed diameter. Thediameters of these devices obviously vary with the size of the bodylumen into which they are placed. For instance, the stents of thisinvention may range in size (for neurological applications) from 2.0 mmin diameter to 30 mm in diameter (for placement in the aorta). A rangeof about 2.0 mm to 6.5 mm (perhaps to 10.0 mm) is believed to bedesirable. Typically, expansion ratios of 2:1 or more are required.These stents are capable of expansion ratios of up to 5:1 for largerdiameter stents. Typical expansion ratios for use with the stents-graftsof the invention typically are in the range of about 2:1 to about 4:1although the invention is not so limited. The thickness of the stentmaterials obviously varies with the size (or diameter) of the stent andthe ultimate required yield strength of the folded stent. These valuesare further dependent upon the selected materials of construction. Wireused in these variations are typically of stronger alloys, e.g., nitinoland stronger spring stainless steels, and have diameters of about 0.002inches to 0.005 inches. For the larger stents, the appropriate diameterfor the stent wire may be somewhat larger, e.g., 0.005 to 0.020 inches.For flat stock metallic stents, thicknesses of about 0.002 inches to0.005 inches is usually sufficient. For the larger stents, theappropriate thickness for the stent flat stock may be somewhat thicker,e.g., 0.005 to 0.020 inches.

The stent-graft is fabricated in the expanded configuration. In order toreduce its diameter for delivery the stent-graft would be folded alongits length, similar to the way in which a PCTA balloon would be folded.It is desirable, when using super-elastic alloys which are also havetemperature-memory characteristics, to reduce the diameter of the stentat a temperature below the transition-temperature of the alloys. Oftenthe phase of the alloy at the lower temperature is somewhat moreworkable and easily formed. The temperature of deployment is desirablyabove the transition temperature to allow use of the super-elasticproperties of the alloy.

As a generic explanation of the mechanical theory of a stent suitablefor use in this invention, reference is made to FIGS. 1A, 1B, 1C, 1D,1E, 2, 3, and 4.

FIG. 1A is a plan view of an isolated section of the stent which may beused in the stent-graft of the invention. The Figure is intended both toidentify a variation of the invention and to provide conventions fornaming the components of the torsion member (100). FIG. 1A shows, inplan view, an undulating torsion member (100) formed from a wire stockinto a U-shape. A torsion pair (102) is made up of an end member (104)and two adjacent torsion lengths (106). Typically, then, each torsionlength (106) will be a component to each of its adjacent torsion pairs(102). The U-shaped torsion pair (102) may be characterized by the factthat the adjacent torsion lengths are generally parallel to each otherprior to formation into the stent.

Generically speaking, the stents of this invention use undulatingtorsion members which are “open” or “unconfined” at their apex or endmember (104). By “open” or “unconfined” we mean that the apex or endmember (104) does not have any means in that apex which would tend toinhibit the movement of the flexible linkage (discussed below) downbetween the arms or torsion lengths (106) of the torsion pair (102).

FIG. 1B shows another variation of the stent having a sinusoidal shapedtorsion member (108). In this variation, the adjacent torsion lengths(110) are not parallel and the wire forms an approximate sinusoidalshape before being formed into a cylinder.

FIG. 1C shows a variation of the stent having an ovoid shaped torsionmember (112). In this variation, the adjacent torsion lengths (114) areagain not parallel. The wire forms an approximate open-ended oval witheach torsion pair (116) before being formed into a cylinder.

FIG. 1D shows another variation of the stent having a V-shaped torsionmember (118). In this variation, the adjacent torsion lengths (120) forma relatively sharp angle at the torsion end (999) shape before beingformed into a cylinder.

FIG. 1E shows a variation in which adjacent torsion members on the stent(117) have differing amplitude. The peaks of the high amplitude torsionmembers (119) may be lined up “out of phase” or “peak to peak” withshort amplitude (121) or high amplitude torsion members in the adjacentturn of the helix or may be positioned “in phase” similar to thosediscussed with regard to FIG. 2 below.

The configurations shown in FIGS 1A-1E are exceptionally kink-resistantand flexible when flexed along the longitudinal axis of the stent.

As ultimately deployed, a section of the torsion member found on one ofFIGS. 1A-1D would be helically wound about a form of an appropriate sizeso that the end members (e.g., 104 in FIG. 1A) would be centered betweenthe end members of the torsion member on an adjacent turn of the helix.This is said to be “in phase”. “Out of phase” would be the instance inwhich the adjacent members meet directly, i.e., end member-to-endmember. In any event, once so aligned, the phasic relationship may bestabilized by weaving a flexible linkage through the end members fromone turn of the helix to the next.

FIG. 2 shows a side view of one typical stent (122) made according tothis invention including the phased relationship of the helical turns ofthe stent and the flexible linkage (124).

FIG. 3 shows a close-up of the FIG. 2 stent and depicts the phasedrelationship (within box A) and shows in detail a typical way in whichthe flexible linkage (124) is looped through the various end members(104) to maintain the phased relationship. It may be noted that theflexible linkage (124) is free to move away from the apex at the endmembers (104) without constraint.

FIG. 4 shows a magnified portion of a stent-graft (viewed from theoutside of the stent-graft) incorporating a stent such as is shown inFIGS. 2 and 3 and depicts a method for distributively attaching thestent to the graft component. Specifically, end member or apex (104) isflanked by side lengths (106) and is looped therethrough by a filament(124). The graft component (134) is seen in the background. The filament(124) adheres to the graft (134) at the locations of contact (130)between the filament (124) and the graft component (134). It should beapparent that the apexes (104) are free to move in the direction shownby arrows (132) when the stent-graft is flexed. This shows the abilityof the various apexes to move longitudinally with respect to each otherand yet retain the graft component (134) reasonably snug against theinner surface of the stent and thereby prevent kinking of that graftcomponent (134).

FIG. 5 shows a close-up of a section of a stent-graft according to theinvention that is similar to the stent-graft portion shown in FIG. 4 butin which the stent is attached to the graft using loops (136) or eyeletson the stent. Again this shows a manner of distributively attaching thestent to the graft component (134). Again, end member or apex (104) isflanked by side lengths (106). Although no filament (124 in FIG. 4) isshown in the variation in FIG. 5, it is contemplated that the filament(124) may be used in conjunction with loops (136). The graft component(134) is seen in the background. These loops (136) may be of a materialwhich adheres to the graft component (134) at the junctions shown at(138). It is also contemplated that the filament (124) may be ofmaterial which is either adherent to (such as a melt-misciblethermoplastic polymer) or not adherent to (such as a metal or thermosetpolymer) the graft component (134) when used with the loops (136).

The scope of materials for the filament (124), graft component (134),and loops (136) will be discussed in detail below.

FIG. 6 shows, in side view, a variation of the stent (140) supportstructure made from wire and having flares (142) at one or both ends.The flaring provides a secure anchoring of the resulting stent-graft(140) against the vessel wall and prevents the implant from migratingdownstream. In addition, the flaring provides a tight seal against thevessel so that the blood is channelled through the lumen rather thanoutside the graft. The undulating structure may vary in spacing to allowthe helix turns to maintain their phased relationship between turns ofthe helix and to conform to the discussion just above. A flexiblelinkage between the contiguous helical turns is not shown but may alsobe applied to at least a portion of the helices.

The stent support structure may also be made by forming a desiredstructural pattern out of a flat sheet. The sheet may then be rolled toform a tube. FIG. 7 shows a plan view of torsion members (160) which maybe then rolled about an axis to form a cylinder. As is shown in FIG. 8,the end caps (162) may be aligned so that they are “in phase”. Theflexible linkage (164) may then be included to preserve the diameter ofthe stent. The graft component (166) is shown on the inner surface ofthe stent. Loops may be used as was described above. The graft may beattached to the loops or filament in the manner discussed above.

The stent shown in FIG. 8 may be machined from tubing. If the chosenmaterial in nitinol, careful control of temperature during the machiningstep may be had by EDM (electro-discharge-machining), laser cutting,chemical machining, or high pressure water cutting.

FIG. 9 is a conceptual schematic of an isolated ring section of anothervariation of the stent component useful in this invention. The FIG. 9 isintended only to identify and to provide conventions for naming thecomponents of the ring. FIG. 9 shows, in plan view, of the layout of thevarious components of a ring as if they were either to be cut from aflat sheet and later rolled into tubular formation for use as a stentwith welding or other suitable joining procedures taking place at theseam or (if constructed from tubing) the layout as if the tubing was cutopen. The portion of the stent between tie members (170) is designatedas a ring (172) or ring section. Tie members (170) serve to link onering (172) to an adjacent ring (172). A torsion pair (174) is made up ofa cap member (176) and two adjacent torsion members (178). Typically,then, each torsion member (178) will be a component to each of itsadjacent torsion pairs (174).

As ultimately deployed, a roll of the sheet found in FIG. 9 would beentered into the body lumen. Typically, it would be folded in somefashion which will be discussed below. A front quarter perspective viewof the rolled stent (179) is shown in the FIG. 10.

FIG. 11 shows a variation of the stent having a ring section (180)similar in configuration to that shown above and joined by tie members(182). Those tie members (182) extend from the inside of a torsion pair(184) to the outside of a torsion pair (186) in the adjacent ringsection. The tie members (182) experience no twisting because of theirplacement in the middle of end cap (188). The tie members may be offseton the end cap, if so desired, to allow the tie members to accept someof the twisting duty.

FIG. 12 shows a plan view of a variation of the inventive stent in whichthe number of torsion members (190) in a selected ring member (192) isfairly high. This added number of torsion members may be due to avariety of reasons. For instance, the material of construction may havea significantly lower tolerance for twisting than the materials in thoseprior Figures. Adding more torsion bars lessens the load carried on eachof the several bars. Alternatively, for the same material, the stent mayneed be folded to a smaller diameter for deployment than those earliervariations.

FIG. 13 shows a variation of the invention (156) in which the end caps(194) are bound by a long torsion member (195) and two short torsionmembers (196). This torsion set (197) is in turn separated from theadjacent torsion set (197) by a bridge member (198) which shares thebending load of the stent when the stent is rolled and the ends (199)joined by, e.g., welding. The short torsion members (196) have a greaterwidth than that of the long torsion member (195) so to balance the loadaround the ring during deformation and thereby to prevent the bridgemembers from becoming askew and out of the ring plane.

It should be clear that a variety of materials variously metallic, superelastic alloys, and preferably nitinol, are suitable for use in thesestents. Primary requirements of the materials are that they be suitablyspringy even when fashioned into very thin sheets or small diameterwires. Various stainless steels which have been physically, chemically,and otherwise treated to produce high springiness are suitable as areother metal alloys such as cobalt chrome alloys (e.g., ELGILOY),platinum/tungsten alloys, and especially the nickel-titanium alloysgenerically known as “nitinol”.

Nitinol is especially preferred because of its “super-elastic” or“pseudo-elastic” shape recovery properties, i.e., the ability towithstand a significant amount of bending and flexing and yet return toits original form without deformation. These metals are characterized bytheir ability to be transformed from an austenitic crystal structure toa stress-induced martensitic structure at certain temperatures, and toreturn elastically to the austenitic shape when the stress is released.These alternating crystalline structures provide the alloy with itssuper-elastic properties. These alloys are well known but are describedin U.S. Pat. Nos. 3,174,851, 3,351,463, and 3,753,700. Typically,nitinol will be nominally 50.6% (±0.2%) Ni with the remainder Ti.Commercially available nitinol materials usually will be sequentiallymixed, cast, formed, and separately cold-worked to 30-40%, annealed, andstretched. Nominal ultimate yield strength values for commercial nitinolare in the range of 30 psi and for Young's modulus are about 700 Kbar.

The '700 patent describes an alloy containing a higher iron content andconsequently has a higher modulus than the Ni-Ti alloys.

Nitinol is further suitable because it has a relatively high strength tovolume ratio. This allows the torsion members to be shorter than forless elastic metals. The flexibility of the stent-graft is largelydictated by the length of the torsion member components in the stentstructural component. The shorter the pitch of the device, the moreflexible the stent-graft structure can be made. Materials other thannitinol are suitable. Spring tempered stainless steels andcobalt-chromium alloys such as ELGILOY are also suitable as are a widevariety of other known “super-elastic” alloys.

Although nitinol is preferred in this service because of its physicalproperties and its significant history in implantable medical devices,we also consider it also to be useful in a stent because of its overallsuitability with magnetic resonance imaging (MRI) technology. Many otheralloys, particularly those based on iron, are an anathema to thepractice of MRI causing exceptionally poor images in the region of thealloy implant. Nitinol does not cause such problems.

Other materials suitable as the stent include certain polymericmaterials, particularly engineering plastics such as thermotropic liquidcrystal polymers (“LCP's”). These polymers are high molecular weightmaterials which can exist in a so-called “liquid crystalline state”where the material has some of the properties of a liquid (in that itcan flow) but retains the long range molecular order of a crystal. Theterm “thermotropic” refers to the class of LCP's which are formed bytemperature adjustment. LCP's may be prepared from monomers such asp,p′-dihydroxy-polynucleararomatics or dicarboxy-polynuclear-aromatics.The LCP's are easily formed and retain the necessary interpolymerattraction at room temperature to act as high strength plastic artifactsas are needed as a foldable stent. They are particularly suitable whenaugmented or filled with fibers such as those of the metals or alloysdiscussed below. It is to be noted that the fibers need not be linearbut may have some preforming such as corrugations which add to thephysical torsion enhancing abilities of the composite.

The flexible linkage between adjacent turns of the helix (124 in FIGS.2, 3, 4, and 8) or the loops (136 in FIG. 5) may be of any appropriatefilamentary material which is blood compatible or biocompatible andsufficiently flexible to allow the stent to flex and not deform thestent upon folding. Although the linkage may be a single or multiplestrand wire (platinum, platinum/tungsten, gold, palladium, tantalum,stainless steel, etc.), much preferred in this invention is the use ofpolymeric biocompatible filaments. Synthetic polymers such aspolyethylene, polypropylene, polyurethane, polyglycolic acid,polyesters, polyamides, their mixtures, blends, copolymers, mixtures,blends and copolymers are suitable; preferred of this class arepolyesters such as polyethylene terephthalate including DACRON and MYLARand polyaramids such as KEVLAR, polyfluorocarbons such aspolytetrafluoroethylene with and without copolymerizedhexafluoropropylene (TEFLON or GORETEX), and porous or nonporouspolyurethanes. Natural materials or materials based on natural sourcessuch as collagen may also be used is this service.

As will be discussed below, the material chosen for the linkage or theloops is preferably of a material which can be bonded to the graft linerin a distributed sequence of points along the outside surface of thegraft liner. By bonding the liner to the linkage or the loops in suchfashion, the flexibility and resistance to kinking of the stent ismaintained in the resulting stent-graft. To state the central concept ofthe invention in another way, the graft component is to bedistributively attached to the stent structure at a number of sites. Theattachments should allow some movement between the graft component andthe stent at the attachment points. This may be accomplished by causingadherence of the graft independently to at least some of the linkage, tothe loops, or to one or the other. Other structural attachments may beused to meet the functional requirements recited here.

Tubular Component Materials

The tubular component or graft member of the stent-graft may be made upof any material which is suitable for use as a graft in the chosen bodylumen. Many graft materials are known, particularly known are those usedas vascular graft materials. For instance, natural materials such ascollagen may be introduced onto the inner surface of the stent andfastened into place. Desirable collagen-based materials include thosedescribed in U.S. Pat. No. 5,162,430, to Rhee et al, and WO 94/01483(PCT/US93/06292), the entirety of which are incorporated by reference.Synthetic polymers such as polyethylene, polypropylene, polyurethane,polyglycolic acid, polyesters, polyamides, their mixtures, blends,copolymers, mixtures, blends and copolymers are suitable; preferred ofthis class are polyesters such as polyethylene terephthalate includingDACRON and MYLAR and polyaramids such as KEVLAR, polyfluorocarbons suchas polytetrafluoroethylene with and without copolymerizedhexafluoropropylene (TEFLON or GORETEX), and porous or nonporouspolyurethanes. Especially preferred in this invention are the expandedfluorocarbon polymers (especially PTFE) materials described in British.Pat. Nos. 1,355,373, 1,506,432, or 1,506,432 or in U.S. Pat. No.3,953,566, U.S. Pat. No. 4,187,390, or U.S. Pat. No. 5,276,276, theentirety of which are incorporated by reference.

Included in the class of preferred expanded fluoropolymers arepolytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP),copolymers of tetrafluoroethylene (TFE) and per fluoro(propyl vinylether) (PFA), homopolymers of polychlorotrifluoroethylene (PCTFE), andits copolymers with TFE, ethylene-chlorotrifluoroethylene (ECTFE),copolymers of ethylene-tetrafluoroethylene (ETFE), polyvinylidenefluoride (PVDF), and polyvinyfluoride (PVF). Especially preferred,because of its widespread use in vascular prostheses, is expanded PTFE.

In addition, one or more radio-opaque metallic fibers, such as gold,platinum, platinum-tungsten, palladium, platinum-iridium, rhodium,tantalum, or alloys or composites of these metals like may beincorporated into the device, particularly, into the graft, to allowfluoroscopic visualization of the device.

The tubular component may also be reinforced using a network of smalldiameter fibers. The fibers may be random, braided, knitted, or woven.The fibers may be imbedded in the tubular component, may be placed in aseparate layer coaxial with the tubular component, or may be used in acombination of the two.

Production of the Stent-Graft

The preferred method of constructing the stent-graft is to firstconstruct the stent incorporating a filamentary linkage of the typediscussed above and then to place the tubular component inside thestent. The tubular component is then expanded using a mandrel or thelike and heated to allow the materials of the filamentary linkage andthe tubular graft component to merge and self-bind.

Loops may be molded into or glued onto the graft component and laterattached to the stent or linkage or the loops may be independentlyintroduced and tied onto the stent structure.

Deployment of the Invention

When a stent-graft having torsion members is folded, crushed, orotherwise collapsed, mechanical energy is stored in torsion in thosetorsion members. In this loaded state, the torsion members have a torqueexerted about them and consequently have a tendency to untwist.Collectively, the torque exerted by the torsion members as folded downto a reduced diameter must be restrained from springing open. The stenttypically has at least one torsion member per fold to take advantage ofthe invention. The stent-graft is folded along its longitudinal axis andrestrained from springing open. The stent-graft is then deployed byremoving the restraining mechanism, thus allowing the torsion members tospring open against the vessel wall.

The attending physician will choose a stent or stent-graft having anappropriate diameter. However, inventive devices of this type aretypically selected having an expanded diameter of up to about 10%greater than the diameter of the lumen to be the site of the stentdeployment.

The stent-graft may be tracked through the vasculature to the intendeddeployment site and then unfolded against the vessel lumen. The grafttube component of the stent-graft is flexible and easy to fold. Foldingor otherwise collapsing the stent structure allows it to return to acircular, open configuration.

FIGS. 14A-14C show a method for deployment of the devices of the presentinvention and allow them to self-expand. FIG. 11A shows a target site(202) having, e.g., a narrowed vessel lumen. A guidewire (204) having aguide tip (206) has been directed to the site using known techniques.The stent-graft (208) is mounted on guidewire (204) and is held in placeprior to deployment by distal barrier (210) and proximal barrier (212).The distal barrier (210) and proximal barrier (212) typically areaffixed to the guidewire tube (214). The tether wire (216) is shownextending through loops (218) proximally through the catheter assembly's(220) outer jacket (222) through to outside the body.

FIG. 14B shows the removal of the tether wire (216) from a portion ofthe loops (218) to partially expand the stent-graft (208) onto theselected site (202).

FIG. 14C shows the final removal of the tether wire (216) from the loops(218) and the retraction of the catheter assembly (220) from theinterior of the stent-graft (208). The stent-graft (208) is shown asfully expanded.

Other methods of deployment are suitable for use with this device andare described in U.S. patent application Ser. Nos. 07/927,165 and07/965,973, the entirety of which are incorporated by reference.

Many alterations and modifications may be made by those of ordinaryskill in the art without departing from the spirit and scope of theinvention. The illustrated embodiments have been shown only for purposesof clarity and examples, and should not be taken as limiting theinvention as defined by the following claims, which include allequivalents, whether now or later devised.

We claim as our invention:
 1. A device comprising: a support componenthaving multiple turns of an undulating member, said member being formedfrom a single continuous wire, each turn of said undulating memberhaving multiple undulations defining multiple apexes, with undulationsin one turn generally in-phase with undulations in an adjacent turn; anda tubular graft component substantially coaxial with said supportcomponent, said tubular graft component being attached to said supportcomponent only in-part, allowing unattached apexes to movelongitudinally relative to said graft component; and said supportcomponent being slidably secured to said graft component such thatrelative movement therebetween is limited.
 2. A device comprising: asupport component comprising multiple turns of an undulating member,said member being formed from a single continuous wire, each turn ofsaid undulating member having multiple undulations which define multipleapexes, wherein undulations in one turn are generally in-phase withundulations in an adjacent turn; and a tubular graft componentpositioned substantially coaxially within said support component, saidtubular graft component being attached to said support component toallow said apexes to move longitudinally relative to said graftcomponent.
 3. The device of claim 2 wherein said member is a helicalmember configured to form said support component and which forms saidmultiple turns of said support component.
 4. The device of claim 3further comprising at least one flexible link, said flexible linkcoupling adjacent helical turns of said support component to maintainsaid undulations generally in-phase.
 5. The device of claim 4, whereinsaid flexible link is secured to said graft component at least in-part.6. The device of claim 2 further comprising at least one loop passingaround at least a portion of one of said undulations to attach saidsupport component to said graft component.
 7. The device of claim 2wherein the support component comprises wire and the undulations have asinusoidal shape.
 8. The device of claim 2 wherein the support componentcomprises wire and the undulations are U-shaped.
 9. The device of claim2 wherein the support component comprises wire and the undulations areV-shaped.
 10. The device of claim 2 wherein the support componentcomprises wire and the undulations are ovaloid shaped.
 11. The device ofclaim 2 wherein the support component comprises a stainless steelmaterial or a titanium alloy.
 12. The device of claim 2 wherein thesupport component comprises a nickeltitanium alloy.
 13. The device ofclaim 2 wherein the tubular graft component comprises polyethyleneterephthalate.
 14. The device of claim 2 wherein the tubular graftcomponent comprises polytetrafluoroethylene.
 15. The device of claim 14wherein the polytetrafluoroethylene is expanded.
 16. The device of claim14 wherein the polytetrafluoroethylene includes hexafluoropropylene. 17.The device of claim 2 wherein the tubular graft comprises apolyfluorocarbon.
 18. The device of claim 2 further comprisingradiopaque markers within said tubular graft member.
 19. A stent-graftcomprising: a self expanding stent comprising an undulating member, saidmember being formed from a single continuous wire arranged in a helicalconfiguration with multiple turns and having multiple undulations, eachundulation having an apex, undulations in adjacent turns being generallyin-phase with one another; and a graft positioned substantiallycoaxially within said stent, said graft being attached to said stent toallow said apexes to move longitudinally relative to said graft.
 20. Thedevice of claim 19 further comprising at least one flexible link, saidflexible link coupling adjacent helical turns of said support componentto maintain said undulations generally in-phase.
 21. The device of claim19 wherein the stent comprises a stainless steel material or a titaniumalloy.
 22. The device of claim 19 wherein the stent comprises astainless steel material or a titanium alloy.
 23. The device of claim 19wherein the graft comprises a polyfluorocarbon.